Okay, so what are the results of:
$ grep kraken@example /var/log/mail.log
Also check the rotated log:
$ grep kraken@example /var/log/mail.log.1
postgrey is doing is filtering out spam by forcing sending servers to follow the published standards on mail servers, and the vast majority of spam servers do not have this capability. The standard states when when receiving a defined response from the receiving server that says “try back later”, the sending server is supposed to try again later. On the retry,
postgrey will pass the email and it will be delivered, assuming it passes other checks.
However, some not-spam sending servers are configured to not re-send, and other not-spam sending servers are part of very complex server pools that re-send from different servers each retry. In both cases, we have to change how
postgrey handles the email, and usually the solutions are different.
In your case, since you are using an alias, you could create the file
/etc/postfix/postgrey_whitelist_recipients and add
email@example.com to the file, then restart
You may consider slightly changing your email address to something like
firstname.lastname@example.org. While I’m not big on security through obscurity, spammers to try guessing things like this.
Note that if you read that Kraken has suffered a breach of email address database, you should switch the account to a different email address and replace the one in the whitelist, because you are about to get spammed.